1. Field of the Invention
The present invention relates generally to a process for increasing the dyeability of polymer materials, and more particularly to a process for improving the dyeability of hydrophobic polymer materials with water-based dyes.
2. Description of the Related Art
The colorability, or dyeability, of polymer materials is dependent upon the chemical and physical properties of the polymers. As used herein, the term xe2x80x9cpolymer materialxe2x80x9d may refer to a single strand of polymer fiber, a web of polymer fibers, a fabric of polymer fibers, a polymer film, or any portion thereof, whether knitted, woven, or nonwoven. As used herein, the term xe2x80x9chydrophobic polymer materialxe2x80x9d includes any polymer material that exhibits hydrophobic characteristics.
Certain polymers are able to be readily colored, or dyed, through submersion with dyeing agents including dyes. As used herein, the term xe2x80x9cdyesxe2x80x9d includes acidic, basic, neutral, disperse, direct, sulfur, azoic, reactive, and vat dyes, inks, and pigments, whether natural, synthetic, water soluble, or water dispersible. A polymer""s dyeability is due to the presence of either receptor groups chemically present in the molecular structure of the polymer, the predominate presence of noncrystalline regions in the polymer""s molecular structure, or both. The presence and reactivity of these receptor groups and/or the presence of noncrystalline regions is often a determinate to the amount of dye, and therefore the color, which can be adsorbed and possibly absorbed by the polymer. Typically, polymers having water-soluble receptor groups (i.e., hydrophilic polymers) are typically more easily dyed than polymers devoid of such groups (i.e., hydrophobic polymers). Similarly, polymers predominately comprised of noncrystalline regions are more easily dyed than polymers exhibiting tightly packed crystalline structures.
Fibers that are chemically comprised of polar functional groups in their molecular structure are often dyeable since the polar groups serve as active receptor sites for the attraction of dye molecules. For example, it is known that cotton comprises hydroxyl groups that act as strong polar functional groups. The hydroxyl groups attract and bond with dye molecules, such that cotton fibers that are submerged in an aqueous dye solution adsorb both dye and water molecules. The adsorbed water molecules cause the cotton fibers to swell such that the dye molecules may then diffuse into the molecular structure of the cotton fiber and thereby effect a color change to the cotton material.
Fiber-forming polymers often physically exhibit crystalline and noncrystalline regions in their structure. In the crystalline regions, polymer molecules are orderly and tightly packed. In the noncrystalline regions (i.e., amorphous regions), polymer molecules are often randomly arranged which thereby enables dye molecules to penetrate the molecular structure of the polymer, along with water molecules, under certain environmental conditions.
Polypropylene (PP) and polyethylene teraphthalate (PET) spunbond (SB) nonwovens are the world""s leading synthetic materials due to their inherent characteristics of strength, resistance to abrasion, resiliency, reasonably low cost, and material-forming characteristics. The popularity and integration of these fabrics into the marketplace are exemplified by the annual production volumes of PP and PET, which are estimated to exceed 50 million tons and 5 million tons, respectively. However, since both PP and PET are hydrophobic, dyeing these polymer materials with water-based dyes has proven extremely difficult.
It is known that PP molecules are comprised of highly crystalline molecular chains are devoid of polar functional groups, and are therefore hydrophobic. Any interaction of dye molecules with PP material results from Van der Waals effects which are sufficiently weak such that dye molecules are often easily washed from the material with water. Consequently, PP molecules are difficult to dye since the dye molecules may not be chemically bonded by adsorption onto the polymer material.
It is also known that PET molecules are comprised of molecular chains which have polar ester (xe2x80x94COOR) groups in their molecular repeat units. Due to the extreme weakness of these ester groups, PET materials, characteristically, are essentially devoid of polar functional groups and are therefore also hydrophobic. Further, PET macromolecules are predominately crystalline in structure, such that a high degree of inter-chain bonding results causing a high glass transition temperature which is further indicative of poor dyeability. Thus, PET materials are relatively chemically inert, and less penetrable to solvents and dyes.
It is known to color PP materials by adding dye pigment to the resin prior to extrusion and melt spinning of the polymer. However, use of this method requires additional coloring times for non-standard colors. This method further limits the recoloration of dyed materials since the material is already extruded with a dye pigment incorporated therein. Further, it is often cost prohibitive to have small quantities of PP material undergo this process.
It is known to dye PET materials using the Thermosol(copyright) process (registered trademark of E. I. DuPont, Wilmington, Del.) which is a pad-dry-bake process consuming high energy. It is also known to dye PET materials using phenol-based organic compounds with disperse dyes. The organic compound acts as a carrier for dye on the PET material and causes the material to swell which thereby enables non-water-soluble, disperse dyes to enter and color the material by a diffusion process. It is further known that the use of these organic compounds and the resulting waste from the manufacturing processes are both odorous and environmentally damaging. These organic compounds, and their effluents, must therefore undergo treatment at the end of the dyeing process. As a result, dyeing PET materials using phenol-based organic compounds results in higher manufacturing costs, air pollution, and the wasteful use of high volumes of water for effluent cleansing at the end of the manufacturing process.
It is also known to dye PET materials using non-water-soluble, disperse dyes above atmospheric pressure with relatively high heat. However, this process requires both special equipment (e.g., closed pressure chambers) and significant amounts of energy to reach higher pressures and temperatures, thereby adding additional costs to the process.
The present invention is directed to a plasma treatment process for modifying the surface characteristics of hydrophobic materials such that the treated materials exhibit increased dyeability with water-based dyes and the resulting modified hydrophobic polymer material having increased dyeability surface properties with water-based dye. The present invention is further directed to dyed hydrophobic polymers having been treated with the plasma process. Accordingly, the plasma treatment process and the modified material provide for efficient, cost-effective dyeability of hydrophobic polymers with water-based dyes.
According to the present invention, a hydrophobic polymer material is treated with a plasma treatment process to provide a hydrophobic polymer material having a modified surface and an improved dyeability with water-based dyes. Preferably, the plasma treatment occurs at about atmospheric pressure (e.g., about 696 Torr or other near atmosphere pressure). Typically, hydrophobic polymers and polymer materials treatable by the invention comprise PP, PET, polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene (PE), polyester, multicomponent combinations of the aforementioned polymers, and multicomponent combinations of the polymers with Kevlar(copyright) or Aramid(copyright) (each is a registered trademark of E. I Dupont, Wilmington, Del.) material. As used herein the term xe2x80x9cmulticomponentxe2x80x9d refers to a composite material made of at least two different polymers extruded together. The resulting multicomponent composite material may have a core of at least one of the polymers within a sheath having at least one of the other polymers. For example, a bicomponent composite material, i.e., a particular type of multicomponent composite material comprising two different types of polymers, may have a core of one type of polymer within a sheath having another type of polymer. Alternatively, multicomponent composite materials may have two or more different types of extruded polymers that are physically side-by-side, as opposed to having a core-sheath configuration.
The present invention provides a method of treating hydrophobic polymer materials using a high-pressure glow discharge plasma treatment to modify the surfaces of the hydrophobic polymer materials to contain polar hydrophilic functional groups. As used herein, the term xe2x80x9chigh-pressurexe2x80x9d refers to a pressure of about 50 Torr or greater. The hydrophobic polymer materials are preferably modified by a high-pressure glow discharge plasma generated in a working gas comprising SO2, O2, N2, He, H2, CO2, CF4, NO, N2O, 2-Hydroxypropyl Methacrylate (HPMA), air, or a combination thereof.
The present invention also includes the resulting modified polymer having undergone plasma treatment such that the surface of the polymer is modified to yield improved dyeability characteristics with water-based dyes. According to the present invention, modified polymers having polarly active sites are better suited to be dyed using water-based dyes. PET and PP materials that undergo treatment by a high-pressure glow discharge plasma demonstrate significantly improved dyeability with water-based dyes due to the presence of hydrophilic functional groups on the polymer surface. Additionally, polymer material that undergo treatment by a high-pressure glow discharge plasma may further demonstrate cationic or anionic characteristics such that polarly-charged dye molecules are attracted to the oppositely-charged functional groups of the modified fiber. Optionally, the modified polymer may be dyed using dyes that are insoluble in water, such as disperse dyes.
The present invention also provides a hydrophobic polymer material having a modified surface with improved dyeability and which is dyed with a water-based dye. Preferably, the hydrophobic polymer material is PP or PET that has been treated with a high-pressure glow discharge plasma.